The invention relates to a plastic pipe used for potable water applications, which is made from a cross-linked polyolefin, preferably but not limited to, polyethylene.
It is advantageous and state-of-the-art to use polyolefins, preferably but not limited to, polyethylene, for making plastic pipes applicable to potable water systems and applications. A further advantage is to use cross-linked polyethylene PEX for making pipes for potable water applications. Such advantages include, but are not limited to, long term stability including oxidation resistance to meet current codes and standards for potable water applications, flexibility in installation including a “memory effect”, etc.
In many countries, potable water is typically more or less chlorinated, chlorine primarily acting as a disinfectant. Chlorinated water environments exhibit additional challenges to plastic pipe systems. It is well known that extensive exposure to chlorine, and/or any of its water-soluble derivatives, at elevated temperatures and pressures, eventually leads to increased failure rates for plastic piping systems through catalyzed oxidation. It is fundamentally established that chlorine, hypochlorite, etc. reacts with polyethylene in an oxidative type of reaction, resulting in undesired and accelerated polymer (pipe) degradation. Typically, antioxidants are used to overcome the degradative effect of chlorine and/or its derivatives. However, it has been discovered that conventional antioxidants, such as Naugard 76 (supplied by Chemtura), which is equal to Irganox 1076 (supplied by Ciba Specialty Chemicals), typically applied with resins currently being used in the manufacture of plastic pipes, may be rapidly consumed through catalyzed oxidation promoted e.g. by chlorinated water, typically being utilized by an end-user in potable water applications. This effect is highly undesirable and may occur in a relatively short period of time. Thus, an immediate need exists for new types of plastic pipe polymer matrix formulations to address the extractability of antioxidants and stabilizers. This may logically be achieved by lowering the rate of diffusion and, consequently, extraction and depletion of said entities.
US 2007/0092675 discloses stabilized polyethylene materials which maintain the physical properties in chlorinated water environments. The disclosure suggests adding antioxidants, such as hindered phenols, phosphates and metal deactivators, to a polyethylene resin. However, the disclosure states that for many applications it is preferred that the resins not be cross-linked. Thus, a need exists for a new type of solution.